Various imaging devices, such as charge-coupled devices (CCD), charge-injection devices (CID), and complementary metal oxide semiconductor (CMOS) imaging devices have been extensively used for imaging scenes in many situations. In some situations, for example, when imaging welding scenes involving bright arcs and molten pools, imaging military activities having ammunition flashes or vehicle headlights, or imaging extra-solar planets having a vastly brighter parent star, the dynamic range of the intensity of light from the scenes can greatly exceed the dynamic range of the imaging device used.
To prevent the imaging device used from being partially or fully saturated, various methods have been used to attenuate the intensity and thereby increase the contrast of the bright areas of the scenes. Such methods comprise shuttering or filtering which globally reduce the intensity of light from the scenes, irrespective of bright areas or dimmer areas of the scenes.
Shuttering is a method for reducing light globally by reducing the exposure time of the imaging devices to the light from the scenes. By mechanically shuttering the light from the scenes to the imaging devices periodically, or by electronically discharging the imaging devices periodically, shuttering globally reduces the total amount of light. Filtering also globally reduces light from the scenes by attenuating light using one or more filters.
Another method of preventing the imaging device from being partially or fully saturated is high intensity light illumination. In high intensity light illumination, dimmer areas of the scenes are illuminated using flashlamps or lasers to provide a more uniform illumination throughout the scene. Shuttering synchronized with the external illumination or other global means of intensity reduction can then be used to bring the dynamic range of the entire scenes into conformity with the dynamic range of the imaging device. However, high intensity light illumination requires high energy consumption. Furthermore, in some situations, for example, imaging extra-solar planets having a vastly brighter parent star, the scenes to be imaged cannot be illuminated using flashlamps or lasers.